1. Field of the Invention
The present invention generally relates to a duplexer using surface acoustic wave filters and an electronic apparatus using the same.
2. Description of the Related Art
Recently, cellular phones and portable information equipment have spread widely along with the development of mobile communications systems. It has been considerable activity in downsizing and improving the terminal equipment among many manufacturers. Some cellular phones deal with both the analog and digital systems and employ a variety of frequency bands such as the 800 MHz-1 GHz band and 1.5 GHz-2.0 GHz band.
The recent development of cellular phones is directed to expanding the terminal functions that follow diversified system specifications. For instance, there are dual-mode cellular phones having the analog and digital systems, and dual-frequency cellular phones conforming to TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access). There are also dual-band cellular phones that handle two bands such as the combination of the 800 MHz band and the 1.9 GHz band, or the combination of the 900 MHz band and the 1.8 GHz or 1.5 GHz band. This trend requires improved performance of parts employed in these cellular phones, such as filters. It is also required to downsize the equipment and reduce the cost.
There are some types of antenna duplexers used in sophisticated terminal equipment. A dielectric type duplexer uses a dielectric for transmit and receive filters. A composite filter uses a dielectric for one to the transmit and receive filters and a surface acoustic wave (SAW) filter for the other. There is yet another type of duplexer that employs SAW filters only. The dielectric type duplexer has a relatively large size and has difficulty in downsizing and thinning the portable terminal equipment. The composite filter has the same problem as mentioned above.
The duplexer with SAW filters has a module type in which filters and a phase matching circuit are mounted on a printed-circuit board. An integral type has a ceramic multilayer package that houses the transmit and receive filters and the phase matching circuit. These filters have a volume approximately equal to ⅓ to 1/15 of that of the dielectric type duplexer and a height approximately equal to ½ to ⅓ of that. The downsized and thinned SAW duplexer can be produced at almost the same cost as the cost of producing the dielectric-type duplexer.
There are several proposals directed to downsizing. Japanese Patent Application Publication No. 10-126213 discloses a multilayer ceramics package and a wiring pattern for phase matching that runs on two layers of the ceramics package. Japanese Patent Application Publication No. 8-18393 discloses another proposal to arrange a phase matching wiring pattern on two layers of a package. Japanese Patent Application No. 10-75153 discloses a phase matching line pattern on multiple layers of a package. Japanese Patent Application No. 2001-339273 discloses phase matching line patterns on an outer wall of a package.
However, these proposals have the following problems. Japanese Patent Application Publication No. 10-1262123 employs wires for making connections with the chip and thus has a problem about downsizing. Further, each of SAW filters of a packaged duplexer needs a respective phase matching circuit.
Japanese Patent Application Publication Nos. 10-1262143 and 8-18393 show the phase matching line is arranged associated with only the antenna terminal and no phase matching line is provided in connection with the transmit and/or receive terminal. It may be considered that the proposals are directed to the 800 MHz band duplexers having less influence of the parasitic impedance of the package than that of the 2 GHz band duplexers. The proposed duplexers do not operate appropriately in the 2 GHz band due to a phase mismatch between the transmit and receive systems.
The duplexer disclosed in Japanese Patent Application No. 10-75153 does not operate appropriately in a high-frequency band such as the 2 GHz band because the phase matching lines associated with the transmit and receive terminals have a single-layer structure.
Japanese Patent Application No. 2001-339273 has a difficulty in downsizing because the phase matching line patterns are provided on the outer walls of the package.